The state of the art relative to vehicle wheel alignment determination has been moving more and more toward electro-mechanical and electro-optical apparatus. The move in that direction has been in most cases motivated by the increasing cost of purely mechanical devices and the need to put operators through sufficient schooling to perform the necessary steps in the use of such apparatus for a reliable result. An example of mechanical apparatus applied to all vehicle wheels has been disclosed by Manlove in U.S. Pat. No. 3,181,248 of May 4, 1965. In this disclosure the apparatus has been arranged for measuring the alignment of the vehicle steerable and non-steerable wheels in which mechanical interconnections, both transversely and longitudinally, are required. Without exhausting examples of prior art, a following generation of wheel aligning apparatus of some pertinence has been set forth by Butler in U.S. Pat. No. 3,865,492 of Feb. 11, 1975. Here the apparatus applied only to the steerable wheels used light projectors and photo-electric receivers mounted in pairs behind a shade so that signals are generated to indicate the angular position of impingment of the light beam.
A further arrangement for determining vehicle wheel alignment using light projectors and mirrors is disclosed by Florer et al in U.S. Pat. No. 4,095,902 of June 20, 1978. The disclosed apparatus combined electronic computing circuits for determining the wheel angles, but the information depended upon the use of mirrors which have known shortcomings. A somewhat similar arrangement of apparatus has been disclosed by Lill in U.S. Pat. No. 4,097,157 of June 27, 1978. More comprehensive alignment apparatus can be found in the copending application of Hollandsworth et al, Ser. Nos. 967,072 filed Dec. 6, 1978 and 023,403 filed Mar. 23, 1979.